Processing apparatus and processing method

ABSTRACT

A processing apparatus configured to process a processing target object includes a modifying device configured to radiate laser light to an inside of the processing target object to form multiple modification layers along a plane direction of the processing target object; and a controller configured to control an operation of the modifying device at least. The controller controls the modifying device to form: a peripheral modification layer which serves as a starting point where a peripheral portion of the processing target object as a removing target is detached; a first internal modification layer in a ring shape to be concentric with the peripheral modification layer at a diametrically inner side than the peripheral modification layer; and a second internal modification layer in a spiral shape at a diametrically inner side than the first internal modification layer.

TECHNICAL FIELD

The various aspects and embodiments described herein pertain generallyto a processing apparatus and a processing method.

BACKGROUND

Patent Document 1 discloses a method in which an internal modificationlayer is formed in a single crystalline substrate, and the substrate iscut using the internal modification layer as a starting point. Accordingto Patent Document 1, the internal modification layer is formed bychanging a single crystalline structure of the substrate into apolycrystalline structure while radiating laser light to an inside ofthe substrate. In addition, in the internal modification layer, adjacentprocessing traces are connected.

PRIOR ART DOCUMENT

Patent Document 1: Japanese Patent Laid-open Publication No.H2013-161820

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Exemplary embodiments provide a technique enabling to perform aperiphery removing processing and a separation processing for aprocessing target object appropriately.

Means for Solving the Problems

In an exemplary embodiment, a processing apparatus configured to processa processing target object includes a modifying device configured toradiate laser light to an inside of the processing target object to formmultiple modification layers along a plane direction of the processingtarget object; and a controller configured to control an operation ofthe modifying device at least. The controller controls the modifyingdevice to form: a peripheral modification layer which serves as astarting point where a peripheral portion of the processing targetobject as a removing target is detached; a first internal modificationlayer in a ring shape to be concentric with the peripheral modificationlayer at a diametrically inner side than the peripheral modificationlayer; and a second internal modification layer in a spiral shape at adiametrically inner side than the first internal modification layer.

Effect of the Invention

According to the exemplary embodiment, it is possible to perform aperiphery removing processing and a separation processing for aprocessing target object appropriately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically illustrating a configuration exampleof a wafer processing system.

FIG. 2 is a side view schematically illustrating an example structure ofa combined wafer.

FIG. 3 is a side view schematically illustrating an example structure ofa part of the combined wafer.

FIG. 4 is a plan view schematically illustrating a configuration exampleof a modifying apparatus.

FIG. 5 is a side view schematically illustrating the configurationexample of the modifying apparatus.

FIG. 6 is a flowchart illustrating an example of main processes of awafer processing.

FIG. 7A to FIG. 7F are explanatory diagrams illustrating the example ofthe main processes of the wafer processing.

FIG. 8 is an explanatory diagram illustrating a state in which aperipheral modification layer is being formed in a processing targetwafer.

FIG. 9 is an explanatory diagram illustrating a state in which theperipheral modification layer is being formed in the processing targetwafer.

FIG. 10 is an explanatory diagram illustrating a state in which aninternal modification layer is being formed in the processing targetwafer.

FIG. 11 is an explanatory diagram illustrating a state in which theinternal modification layer is being formed in the processing targetwafer.

FIG. 12 is an explanatory diagram illustrating a state in which aperiphery of the processing target wafer is being removed.

FIG. 13A and FIG. 13B are explanatory diagrams illustrating a state inwhich a central modification layer is being formed in the processingtarget wafer.

FIG. 14A and FIG. 14B are explanatory diagrams illustrating a state inwhich the processing target wafer is being separated.

FIG. 15A and FIG. 15B are explanatory diagrams illustrating anothermethod of separating the processing target wafer.

FIG. 16 is an explanatory diagram illustrating the formed internalmodification layer.

FIG. 17 is an explanatory diagram illustrating a first eccentricitycorrection method.

FIG. 18 is explanatory diagram illustrating a second eccentricitycorrection method.

FIG. 19 is an explanatory diagram illustrating a method of forming theinternal modification layer in the second eccentricity correctionmethod.

FIG. 20 is an explanatory diagram illustrating a third eccentricitycorrection method.

FIG. 21 is an explanatory diagram illustrating a state in which thecentral modification layer is being formed in the processing targetwafer.

FIG. 22 is an explanatory diagram illustrating another example offorming the central modification layer.

FIG. 23A and FIG. 23B are explanatory diagrams illustrating a method offorming an internal modification layer according to a second exemplaryembodiment.

FIG. 24A and FIG. 24B are explanatory diagrams illustrating the internalmodification layer formed in the second exemplary embodiment.

FIG. 25 is a flowchart illustrating example processes of a waferprocessing according to the second exemplary embodiment.

FIG. 26A to FIG. 26E are explanatory diagrams illustrating the exampleprocesses of the wafer processing according to the second exemplaryembodiment.

FIG. 27A and FIG. 27B are explanatory diagrams illustrating improvementof surface roughness of the processing target wafer.

FIG. 28A and FIG. 28B are explanatory diagrams illustrating otherexamples of the internal modification layer formed according to thesecond exemplary embodiment.

FIG. 29A and FIG. 29B are explanatory diagrams illustrating otherexamples of the internal modification layer formed according to thesecond exemplary embodiment.

DETAILED DESCRIPTION

In a manufacturing process for a semiconductor device, a semiconductorwafer (hereinafter, simply referred to as a wafer) such as a circularsubstrate having a plurality of devices such as electronic circuitsformed on a surface thereof is thinned by radiating laser light to aninside of the wafer to form a modification layer and separating thewafer by using the modification layer as a starting point, as describedin Patent Document 1, for example.

For such wafer separation, after the modification layer is formed withinthe wafer, a tensile force in a detaching direction is applied whileholding a front side and a rear side of the wafer. Accordingly, thewafer is separated and thinned using the formed modification layer andcracks propagating from the modification layer as a boundary. In thefollowing description, among separated wafers, the wafer on the frontside where the devices are formed will be sometimes referred to as a“first separation wafer,” and the wafer on the rear side, as a “secondseparation wafer”.

Further, in the separation of the wafer, an edge trimming processing isperformed to suppress a peripheral portion of the wafer from having asharp pointed shape (a so-called knife edge shape) by the separation. Inthe edge trimming processing, a modification layer is formed byradiating laser light to an inside of the wafer along a peripheralportion of the wafer as a removing target, and the peripheral portion isdetached starting from this modification layer.

However, when performing the separation of the wafer and the removal ofthe peripheral portion thereof as described above, if the modificationlayer is formed eccentrically with respect to the wafer, the separationof the wafer and the removal of the peripheral portion thereof may notbe performed properly. To be specific, if the modification layer for thedetachment is eccentric toward a peripheral side of the wafer, thequality of the removal of the peripheral portion may not be maintained,whereas if the modification layer is eccentric toward a center side ofthe wafer, the separation may not be performed properly. Patent Document1 does not mention anything about this eccentricity of the modificationlayer. Thus, there is a room for improvement.

The present disclosure provides a technique enabling to perform aperiphery removing processing and a separation processing for aprocessing target object appropriately. Hereinafter, a wafer processingsystem equipped with a processing apparatus according to an exemplaryembodiment and a wafer processing method as a processing method will bedescribed with reference to the accompanying drawings. In the presentspecification and the drawings, parts having substantially the samefunctions and configurations will be assigned same reference numerals,and redundant description thereof will be omitted.

First, a configuration of the wafer processing system will be discussed.FIG. 1 is a plan view schematically illustrating a configuration of awafer processing system 1.

The wafer processing system 1 is configured to perform a processing on acombined wafer T in which a processing target wafer W and a supportwafer S are bonded to each other as illustrated in FIG. 2. In the waferprocessing system 1, the processing target wafer W is separated andthinned. Hereinafter, in the processing target wafer W, a surface bondedto the support wafer S will be referred to as a front surface Wa, and asurface opposite to the front surface Wa will be referred to as a rearsurface Wb. Likewise, in the support wafer S, a surface bonded to theprocessing target wafer W will be referred to as a front surface Sa, anda surface opposite to the front surface Sa will be referred to as a rearsurface Sb. Further, in the present exemplary embodiment, the processingtarget wafer W corresponds to a processing target object of the presentdisclosure.

The processing target wafer W is a semiconductor wafer such as, but notlimited to, a silicon wafer having a circular plate shape, and it has,on the front surface Wa thereof, a device layer D including a pluralityof devices such as electronic circuits. Further, an oxide film Fw, forexample, a SiO₂ film (TEOS film) is further formed on the device layerD. In the present exemplary embodiment, the processing target wafer Wconstitutes the aforementioned wafer as the target of separation.

The support wafer S is a wafer that supports the processing target waferW. An oxide film Fs, for example, a SiO₂ film (TEOS film) is formed onthe front surface Sa of the support wafer S. Further, if the supportwafer S has a plurality of devices formed on the front surface Sathereof, a device layer (not shown) is formed on the front surface Sa,the same as in the processing target wafer W.

Further, in the following description, illustration of the device layerD and the oxide films Fw and Fs may be omitted in some cases for thesimplicity of illustration.

Further, in addition to the above-stated thinning processing, an edgetrimming processing is further performed on the processing target waferW to suppress a peripheral portion of the processing target wafer W fromhaving a knife edge shape by the thinning processing as described above.In the edge trimming processing, as shown in FIG. 3, a peripheralmodification layer M1 is formed by radiating laser light to a boundarybetween a peripheral portion We as a removing target and a centralportion Wc, and the peripheral portion We is removed starting from thisperipheral modification layer M1. Further, the peripheral portion We tobe removed by the edge trimming may range from, e.g., 1 mm to 5 mm froman edge of the processing target wafer W in a diametrical directionthereof. A method of the edge trimming processing will be describedlater.

Here, if the processing target wafer W and the support wafer S arebonded in the peripheral portion We of the processing target wafer W,there is a likelihood that the peripheral portion We may not be removedappropriately. For the reason, a non-bonding region Ae for appropriatelyperforming the edge trimming is formed at an interface between theprocessing target wafer W and the support wafer S in a portioncorresponding to the peripheral portion We as the removal target in theedge trimming. Specifically, as shown in FIG. 3, a bonding region Ac inwhich the processing target wafer W and the support wafer S are bondedand the non-bonding region Ae in which bonding strength between theprocessing target wafer W and the support wafer S is reduced are formedat the interface between the processing target wafer W and the supportwafer S. Further, it is desirable that an outer end of the bondingregion Ac is located slightly outer than an inner end of the peripheralportion We to be removed.

The non-bonding region Ae may be formed before the bonding, for example.Specifically, by removing a bonding interface of the processing targetwafer W before being subjected to the bonding through polishing or wetetching, by modifying the bonding interface through radiation of laserlight thereto, or by hydrophobizing the bonding interface throughapplication of a hydrophobic material thereon, the bonding strength isreduced to form the non-bonding region Ae. Further, the “bondinginterface” where the non-bonding region Ae is formed refers to a portionof the processing target wafer W forming an interface to be actuallybonded to the support wafer S.

The non-bonding region Ae may be formed after the bonding, for example.Specifically, by radiating laser light to the interface in a portioncorresponding to the peripheral portion We of the processing targetwafer W after the bonding, the bonding strength for the front surface Saof the support wafer S is reduced, so that the non-bonding region Ae isformed. In addition, the non-bonding region Ae may be formed at anyposition in the vicinity of the bonding interface between the processingtarget wafer W and the support wafer S as long as a bonding forcebetween the processing target wafer W and the support wafer S in theperipheral portion of the processing target wafer W can be appropriatelyreduced. That is, it is assumed that the “vicinity of the bondinginterface” according to the present exemplary embodiment includes theinside of the processing target wafer W, the inside of the device layerD, the inside of an oxide film Fw, and so forth.

As depicted in FIG. 1, the wafer processing system 1 includes acarry-in/out station 2 and a processing station 3 connected as one body.In the carry-in/out station 2, a cassette Ct capable of accommodatingtherein a multiple number of combined wafers T is carried to/from theoutside, for example. The processing station 3 is equipped with variouskinds of processing apparatuses configured to perform requiredprocessings on the combined wafers T.

A cassette placing table 10 is provided in the carry-in/out station 2.In the shown example, a plurality of, for example, three cassettes Ctcan be arranged on the cassette placing table 10 in a row in the Y-axisdirection. Further, the number of the cassettes Ct placed on thecassette placing table 10 is not limited to the example of the presentexemplary embodiment but can be selected as required.

In the carry-in/out station 2, a wafer transfer device 20 is providedadjacent to the cassette placing table 10 at a negative X-axis side ofthe cassette placing table 10. The wafer transfer device 20 isconfigured to be movable on a transfer path 21 which is elongated in theY-axis direction. Further, the wafer transfer device 20 is equippedwith, for example, two transfer arms 22 each of which is configured tohold and transfer the combined wafer T. Each transfer arm 22 isconfigured to be movable in a horizontal direction and a verticaldirection and pivotable around a horizontal axis and a vertical axis.Further, the configuration of the transfer arm 22 is not limited to theexemplary embodiment, and various other configurations may be adopted.The wafer transfer device 20 is configured to be capable of transferringthe combined wafer T to/from the cassette Ct of the cassette placingtable 10 and a transition device 30 to be described later.

In the carry-in/out station 2, the transition device 30 configured todeliver the combined wafer T is provided adjacent to the wafer transferdevice 20 at a negative X-axis side of the wafer transfer device 20.

The processing station 3 is provided with, for example, three processingblocks G1 to G3. The first processing block G1, the second processingblock G2 and the third processing block G3 are arranged side by side inthis sequence from a positive X-axis side (from the carry-in/out station2 side) toward a negative X-axis side.

The first processing block G1 is equipped with an etching apparatus 40,a cleaning apparatus 41, and a wafer transfer device 50. The etchingapparatus 40 and the cleaning apparatus 41 are stacked on top of eachother. Further, the number and the layout of the etching apparatus 40and the cleaning apparatus 41 are not limited to the shown example. Byway of example, the etching apparatus 40 and the cleaning apparatus 41may be arranged side by side in the X-axis direction. Further, aplurality of etching apparatuses 40 and a plurality of cleaningapparatuses 41 may be respectively stacked on top of each other.

The etching apparatus 40 is configured to etch a separated surface ofthe processing target wafer W grounded by a processing apparatus 80 tobe described later. By way of example, by supplying a chemical liquid(etching liquid) onto the separated surface, this separated surface iswet-etched. For instance, HF, HNO₃, H₃PO₄, TMAH, Choline, KOH, or thelike may be used as the chemical liquid.

The cleaning apparatus 41 is configured to clean the separated surfaceof the processing target wafer W grounded by the processing apparatus 80to be described later. By way of example, by bringing a brush intocontact with the separated surface, the separated surface is cleaned bybeing scrubbed. Furthermore, a pressurized cleaning liquid may be usedfor the cleaning of the separated surface. In addition, the cleaningapparatus 41 may be configured to clean the rear surface Sb of thesupport wafer S as well as the separated surface of the processingtarget wafer W.

The wafer transfer device 50 is disposed at, for example, a negativeY-axis side of the etching apparatus 40 and the cleaning apparatus 41.The wafer transfer device 50 has, for example, two transfer arms 51 eachof which is configured to hold and transfer the combined wafer T. Eachtransfer arm 51 is configured to be movable in a horizontal directionand a vertical direction and pivotable around a horizontal axis and avertical axis. Further, the configuration of the transfer arm 51 is notlimited to the exemplary embodiment, and various other configurationsmay be adopted. Additionally, the wafer transfer device 50 is configuredto be capable of transferring the combined wafer T to/from thetransition device 30, the etching apparatus 40, the cleaning apparatus41 and a modifying apparatus 60 to be described later.

The second processing block G2 is equipped with the modifying apparatus60 as a processing apparatus and a wafer transfer device 70. The numberand the layout of the modifying apparatus 60 is not limited to theexample of the present exemplary embodiment, and a plurality ofmodifying apparatuses 60 may be stacked.

The modifying apparatus 60 is configured to form the non-bonding regionAe, the peripheral modification layer M1, an internal modification layerM2, and a central modification layer M3 by radiating laser light to aninside of the processing target wafer W. A detailed configuration of themodifying apparatus 60 will be elaborated later.

The wafer transfer device 70 is disposed at, for example, a positiveY-axis side of the modifying apparatus 60. The wafer transfer device 70is equipped with, for example, two transfer arms 71 each of which isconfigured to hold and transfer the combined wafer T. Each transfer arm71 is supported at a multi-joint arm member 72 and configured to bemovable in a horizontal direction and a vertical direction and pivotablearound a horizontal axis and a vertical axis. Further, the configurationof the transfer arm 71 is not limited to the example of the presentexemplary embodiment, and may vary as required. The wafer transferdevice 70 is configured to be capable of transferring the combined waferT to/from the cleaning apparatus 41, the modifying apparatus 60, and theprocessing apparatus 80 to be described later.

The third processing block G3 is equipped with the processing apparatus80. The number and the layout of the processing apparatus 80 is notlimited to the example of the present exemplary embodiment, and aplurality of processing apparatuses 80 may be arranged as required.

The processing apparatus 80 has a rotary table 81. The rotary table 81is configured to be rotatable about a vertical rotation center line 82by a rotation mechanism (not shown). Two chucks 83 each configured toattract and hold the combined wafer T are provided on the rotary table81. The chucks 83 are arranged on a circle concentric with the rotarytable 81 in a uniform manner. The two chucks 83 are configured to bemoved to a delivery position 80 a and a processing position 80 b as therotary table 81 is rotated. Further, each of the two chucks 83 isconfigured to be rotatable around a vertical axis by a rotatingmechanism (not shown).

At the delivery position 80 a, delivery of the combined wafer T isperformed. The grinding unit 84 is disposed at the processing position80 b to grind the processing target wafer W. The grinding unit 84 isequipped with a grinder 85 having a grinding whetstone (not shown)configured to be rotated in a ring shape. Further, the grinder 85 isconfigured to be movable in a vertical direction along a supportingcolumn 86. While keeping the processing target wafer W held by the chuck83 in contact with the grinding whetstone, the chuck 83 and the grindingwhetstone are respectively rotated.

The above-described wafer processing system 1 is equipped with a controldevice 90 as a controller. The control device 90 is implemented by, forexample, a computer equipped with a CPU, a memory, and so forth, andincludes a program storage (not shown). A program for controlling aprocessing of the processing target wafer Win the wafer processingsystem 1 is stored in the program storage. Further, the program storagealso stores therein a program for implementing a wafer processing to bedescribed later in the wafer processing system 1 by controlling theabove-described various processing apparatuses and a driving system suchas the transfer devices. Further, the programs may be recorded in acomputer-readable recording medium H, and may be installed from thisrecording medium H to the control device 90.

Moreover, the aforementioned various processing apparatus may be furtherequipped with control devices (not shown) respectively configured tocontrol the various processing apparatuses independently.

Now, the aforementioned modifying apparatus 60 will be described. FIG. 4and FIG. 5 are a plan view and a side view illustrating a schematicconfiguration of the modifying apparatus 60, respectively.

The modifying apparatus 60 is equipped with a chuck 100 as a holderconfigured to hold the combined wafer Ton a top surface thereof. Thechuck 100 is configured to attract and hold the rear surface Sb of thesupport wafer S in the state that the processing target wafer W isplaced at an upper side and the support wafer S is placed at a lowerside. The chuck 100 is supported on a slider table 102 with an airbearing 101 therebetween. A rotating mechanism 103 is provided at abottom surface side of the slider table 102. The rotating mechanism 103incorporates therein, for example, a motor as a driving source. Thechuck 100 is configured to be rotated around a vertical axis by therotating mechanism 103 via the air bearing 101 therebetween. The slidertable 102 is configured to be moved by a moving mechanism 104, which isprovided at a bottom surface side of the slider table 102 to serve as aholder moving mechanism, along a rail 105 which is provided on a base106 and elongated in the Y-axis direction. Further, though notparticularly limited, a driving source of the moving mechanism 104 maybe, for example, a linear motor.

A laser head 110 serving as a modifying device is provided above thechuck 100. The laser head 110 has a lens 111. The lens 111 is acylindrical member provided on a bottom surface of the laser head 110,and is configured to radiate the laser light to the processing targetwafer W held by the chuck 100.

The laser head 110 is configured to concentrate and radiate the laserlight having a wavelength featuring transmissivity for the processingtarget wafer W to a preset position within the processing target wafer Was high-frequency laser light in a pulse shape oscillated from a laserlight oscillator (not shown). Accordingly, a portion within theprocessing target wafer W to which the laser light is concentrated ismodified, so that the non-bonding region Ae, the peripheral modificationlayer M1, the internal modification layer M2, and the centralmodification layer M3 are formed.

In the present exemplary embodiment, in order to avoid complication ofillustration, it is assumed that the non-bonding region Ae, theperipheral modification layer M1, the internal modification layer M2,and the central modification layer M3 are formed by the common laserhead 110. However, they may be formed by different laser heads. Inaddition, the laser heads may be used selectively depending on the typeof laser light to be radiated.

The laser head 110 is supported at a supporting member 112. The laserhead 110 is configured to be moved up and down by an elevating mechanism114 along a vertically elongated rail 113. Further, the laser head 110is configured to be moved in the Y-axis direction by a moving mechanism115 as a modifying device moving mechanism. Each of the elevatingmechanism 114 and the moving mechanism 115 is supported at a supportingcolumn 116.

Above the chuck 100, a macro-camera 120 and a micro-camera 121 areprovided at a positive Y-axis side of the laser head 110. For example,the macro-camera 120 and the micro-camera 121 are formed as one body,and the macro-camera 120 is provided at a positive Y-axis side of themicro-camera 121. The macro-camera 120 and the micro-camera 121 areconfigured to be moved up and down by an elevating mechanism 122, andalso configured to be moved in the Y-axis direction by a movingmechanism 123.

The macro-camera 120 is configured to image an outer end portion of theprocessing target wafer W (combined wafer T). The macro-camera 120 isequipped with, for example, a coaxial lens, and radiates visible light,for example, red light and receives reflection light from a targetobject. For example, the macro-camera 120 has an image magnification oftwo times.

The image obtained by the macro-camera 120 is outputted to the controldevice 90. The control device 90 calculates a first eccentric amountbetween a center of the chuck 100 and a center of the processing targetwafer W from the image obtained by the macro camera 120.

The micro-camera 121 is configured to image a peripheral portion of theprocessing target wafer W and image a boundary between the bondingregion Ac and the non-bonding region Ae. The micro-camera 121 isequipped with, for example, a coaxial lens, and radiates infrared light(IR light) and receives reflection light from a target object. By way ofexample, the micro-camera 121 has an image magnification of 10 times. Afield of view of the micro-camera 121 is about ⅕ of a field of view ofthe macro-camera 120, and a pixel size of the micro-camera 121 is about⅕ of a pixel size of the macro-camera 120.

The image obtained by the micro-camera 121 is outputted to the controldevice 90. In the control device 90, a second eccentric amount betweenthe center of the chuck 100 and the center of the bonding region Ac iscalculated from the image obtained by the micro-camera 121. Also, thecontrol device 90 moves the chuck 100 or the laser head 110 based on thesecond eccentric amount so that the center of the chuck 100 and thecenter of the bonding region Ac are coincident with each other. In thefollowing description, this control of moving the chuck 100 or the laserhead 110 will be sometimes referred to as eccentricity correction.

Now, a wafer processing performed by using the wafer processing system 1configured as described above will be discussed. FIG. 6 is a flowchartillustrating main processes of the wafer processing. FIG. 7A to FIG. 7Fare explanatory diagrams illustrating the main processes of the waferprocessing. In the present exemplary embodiment, the combined wafer T ispreviously formed by bonding the processing target wafer W and thesupport wafer S in a bonding apparatus (not shown) at the outside of thewafer processing system 1. Further, although the combined wafer Tcarried into the wafer processing system 1 is already provided with theaforementioned non-bonding region Ae formed thereat, the followingdescription will be provided for an example where the non-bonding regionAe is formed in the modifying apparatus 60.

First, the cassette Ct accommodating therein the multiple number ofcombined wafers T shown in FIG. 7A is placed on the cassette placingtable 10 of the carry-in/out station 2.

Then, the combined wafer T is taken out of the cassette Ct by the wafertransfer device 20, and transferred into the transition device 30.Subsequently, the combined wafer T is taken out of the transition device30 by the wafer transfer device 50, and transferred into the modifyingapparatus 60. In the modifying apparatus 60, the non-bonding region Aeis first formed, as shown in FIG. 7B (process A1 of FIG. 6).Subsequently, a peripheral modification layer M1 is formed inside theprocessing target wafer W, as illustrated in FIG. 7C (process A2 of FIG.6), an internal modification layer M2 is formed, as shown in FIG. 7D(process A3 of FIG. 6), and a central modification layer M3 is formed(process A4 of FIG. 6). The peripheral modification layer M1 serves as astarting point when the peripheral portion We is removed in the edgetrimming. The internal modification layer M2 serves as a starting pointfor separating the processing target wafer W. The central modificationlayer M3 controls development of cracks in the central portion of theprocessing target wafer W, and serves as a starting point for theseparation in the central portion of the processing target wafer W.

In the modifying apparatus 60, the combined wafer T is carried into themodifying apparatus 60 by the wafer transfer device 50, and held on thechuck 100. Then, the chuck 100 is moved to a formation position of thenon-bonding region Ae. The formation position of the non-bonding regionAe is a position where the laser head 110 is capable of radiating thelaser light to the peripheral portion We of the processing target waferW.

Then, by radiating laser light L (for example, CO₂ laser) from the laserhead 110 while rotating the chuck 100 in a circumferential directionthereof, the non-bonding region Ae is formed (process A1 of FIG. 6). Inaddition, as described above, the non-bonding region Ae can be formed atany position near the bonding interface as long as the bonding strengthbetween the processing target wafer W and the support wafer S can bereduced.

Subsequently, the chuck 100 is moved to a macro-alinement position. Themacro-alignment position is a position where the macro-camera 120 iscapable of imaging an outer end portion of the processing target waferW.

Thereafter, the outer end portion of the processing target wafer W isimaged by the macro-camera 120 in 360 degrees in a circumferentialdirection of the processing target wafer W. The obtained image isoutputted to the control device 90 from the macro-camera 120.

In the control device 90, a first eccentric amount between the center ofthe chuck 100 and the center of the processing target wafer W iscalculated from the image obtained by the macro-camera 120. Further, inthe control device 90, a moving amount of the chuck 100 is calculatedbased on the first eccentric amount to correct a Y-axis component of thefirst eccentric amount. The chuck 100 is moved in the Y-axis directionbased on the calculated moving amount, and then moved to amicro-alignment position. The micro-alignment position is a positionwhere the micro-camera 121 is capable of imaging the peripheral portionof the processing target wafer W. Here, the field of view of themicro-camera 121 is smaller (about ⅕) than the field of view of themacro-camera 120, as stated above. Thus, if the Y-axis component of thefirst eccentric amount is not corrected, the peripheral portion of theprocessing target wafer W may not be included in an angle of view of themicro-camera 121, resulting in a failure to image the peripheral portionof the processing target wafer W with the micro-camera 121. For thereason, the correction of the Y-axis component based on the firsteccentric amount is performed to move the chuck 100 to themicro-alignment position.

Subsequently, a boundary between the bonding region Ac and thenon-bonding region Ae is imaged by the micro-camera 121 in 360 degreesin the circumferential direction of the processing target wafer W. Theobtained image is outputted to the control device 90 from themicro-camera 121.

In the control device 90, a second eccentric amount between the centerof the chuck 100 and a center of the bonding region Ac is calculatedfrom the image obtained by the micro-camera 121. Further, in the controldevice 90, the position of the chuck 100 with respect to the peripheralmodification layer M1 is decided based on the second eccentric amountsuch that the center of the bonding region Ac and the center of thechuck 100 are coincident with each other.

Then, the chuck 100 is moved to a modification position. Themodification position is a position where the laser head 110 radiateslaser light to the processing target wafer W to form the peripheralmodification layer M1. Further, in the present exemplary embodiment, themodification position is the same as the micro-alignment position.

Subsequently, as illustrated in FIG. 8 and FIG. 9, by radiating laserlight L (for example, YAG laser) from the laser head 110, the peripheralmodification layer M1 is formed at the boundary between the peripheralportion We and the central portion We of the processing target wafer W(process A2 of FIG. 6). Further, within the processing target wafer W, acrack C1 develops from the peripheral modification layer M1 in athickness direction of the processing target wafer W. The crack C1reaches the front surface Wa but does not reach the rear surface Wb.

A lower end of the peripheral modification layer M1 formed by the laserlight L is located above a surface of the separated processing targetwafer W after being finally processed. That is, the formation positionof the peripheral modification layer M1 is adjusted such that theperipheral modification layer M1 is not left in the first separationwafer W1 after being separated (more specifically, after a grindingprocessing to be described later).

In the process A2, to locate the chuck 100 at the position decided bythe control device 90, the chuck 100 is rotated by the rotatingmechanism 103 so that the center of the bonding region Ac and the centerof the chuck 100 are coincident, and, also, the chuck 100 is moved inthe Y-direction by the moving mechanism 104 (eccentricity correction).At this time, the rotation of chuck 100 and the movement of the chuck100 in the Y-axis direction are synchronized.

While performing the eccentricity correction of the chuck 100(processing target wafer W) as described above, the laser light L isradiated to the inside of the processing target wafer W from the laserhead 110. That is, while correcting the second eccentric amount, theperipheral modification layer M1 is formed. The peripheral modificationlayer M1 is formed in a ring shape to be concentric with the bondingregion Ac. Accordingly, the peripheral portion We can be appropriatelyremoved later, starting from the peripheral modification layer M1 (crackC1).

Further, in the present exemplary embodiment, if the second eccentricamount includes an X-axis component, this X-axis component is correctedby rotating the chuck 100 while moving it in the Y-axis direction.Meanwhile, if the second eccentric amount does not include the X-axiscomponent, the chuck 100 only needs to be moved in the Y-axis directionwithout being rotated.

Thereafter, as depicted in FIG. 10 and FIG. 11, by radiating laser lightL (for example, YAG laser) from the laser head 110, the internalmodification layer M2 is formed along a plane direction of theprocessing target wafer W (process A3 of FIG. 6). Black arrows shown inFIG. 11 indicate a rotation direction of the chuck 100, and a whitearrow indicates a movement direction of a processing point according tothe movement of the chuck 100 or the laser head 110. Further, within theprocessing target wafer W, a crack C2 develops from the internalmodification layer M2 along the plane direction. The cracks C2 developonly inside the peripheral modification layer M1 in the diametricaldirection.

In addition, if the internal modification layer M2 is formed at adiametrically outer side than the peripheral modification layer M1, thequality of the edge trim after the peripheral portion We is removed maybe degraded, as illustrated in FIG. 12. That is, the peripheral portionWe may not be appropriately removed starting from the peripheralmodification layer M1 (crack C1), and a part of the peripheral portionWe may remain on the support wafer S. From this point of view, theformation position of the internal modification layer M2 is adjusted sothat it is formed at a diametrically inner side than the peripheralmodification layer M1.

Furthermore, a lower end of the internal modification layer M2 formed bythe laser light L is located above the surface of the separatedprocessing target wafer W after being finally processed. That is, theformation position of the internal modification layer M2 is adjustedsuch that the internal modification layer M2 is not left within thefirst separation wafer after being separated (more specifically afterthe grinding processing to be described later).

In the process A3, by radiating the laser light L periodically to theinside of the processing target wafer W from the laser head 110 whilerotating the chuck 100 (processing target wafer W) and moving the laserhead 110 in the Y-axis direction from a diametrically outer side of theprocessing target wafer W toward a diametrically inner side thereof, theinternal modification layer M2 is formed in a spiral shape along theplane direction of the processing target wafer W. Details of the methodof forming the internal modification layers M2 will be described later.

In the present exemplary embodiment, in forming the internalmodification layer M2, the chuck 100 or the laser head 110 is moved inthe Y-axis direction. More specifically, between the chuck 100 and thelaser head 100, the same member as moved in the eccentricity correctionis moved. That is, in the formation of the internal modification layerM2, the eccentricity correction and the formation of the internalmodification layer M2 are simultaneously controlled on one axis, as willbe described later. Further, although the chuck 100 is rotated informing the internal modification layer M2, the laser head 110 may bemoved to rotate the laser head 110 relative to the chuck 100.

In addition, when separating the processing target wafer W starting fromthe internal modification layer M2 as will be described later, it isdesirable that an interval (pitch) of the internal modification layersM2 is set to be uniform in order to perform the separation of theprocessing target wafer W uniformly within the surface of the processingtarget wafer W. Thus, in the process A3, by controlling a rotation speedof the chuck 100 and a frequency of the laser light L, the intervalbetween the internal modification layers M2 is adjusted. That is, when aposition of the laser head 110 in the diametrical direction (that is, aradiation position of the laser light L) is located at an outerperiphery of the processing target wafer W, the rotation speed isreduced, whereas when the position of the laser head 110 in thediametrical direction is located at the central portion of theprocessing target wafer W, the rotation speed is increased. In addition,when the position of the laser head 110 in the diametrical direction(that is, the radiation position of the laser light L) is located at theouter periphery of the processing target wafer W, the frequency of thelaser light L is increased, whereas when the position of the laser head110 in the diametrical direction is located at the central portion ofthe processing target wafer W, the frequency is reduced.

If the internal modification layers M2 are formed in the processingtarget wafer W, the laser light L (for example, YAG laser) is radiatedfrom the laser head 110 to form the central modification layers M3 alongthe plane direction of the processing target wafer W, as shown in FIG.13A and FIG. 13B (process A4 of FIG. 6). Within the processing targetwafer W, cracks C3 develop from the central modification layers M3 inthe plane direction. The central modification layers M3 are formed to bespaced apart from each other (for example, 10 μm or more) so that thecracks C3 are not connected to each other and are not connected to thecracks C2.

In the process A4, the rotation of the chuck 100 (processing targetwafer W) is stopped, and by radiating the laser light L from the laserhead 110 to the inside of the processing target wafer W while moving thelaser head 110 in horizontal directions (the X-axis direction and theY-axis direction) above the processing target wafer W, the centralmodification layer M3 is formed in a straight line shape in the planedirection. Details of this method of forming the central modificationlayer M3 in the process A4 will be discussed later.

In the formation of the central modification layer M3, the chuck 100 maybe moved in the horizontal directions instead of the laser head 110.

After the central modification layer M3 is formed in the processingtarget wafer W, the combined wafer T is then carried out of themodifying apparatus 60 by the wafer transfer device 70.

Then, the combined wafer T is transferred into the processing apparatus80 by the wafer transfer device 70. In the processing apparatus 80, whenthe combined wafer T is delivered from the transfer ram 71 onto thechuck 83, the processing target wafer W is separated into the firstseparation wafer W1 and the second separation wafer W2, starting fromthe peripheral modification layer M1 and the internal modification layerM2 (process A5 of FIG. 6), as illustrated in FIG. 7E. At this time, theperipheral portion We is also removed from the processing target waferW. Here, since the non-bonding region Ae is formed in the vicinity ofthe bonding interface between the processing target wafer W and thesupport wafer S, the peripheral portion We can be easily detached, sothat the separation of the processing target wafer W can be carried outappropriately.

In the process A5, the support wafer S is attracted to and held by thechuck 83 while the processing target wafer W is attracted to and heldwith an attraction surface 71 a of the transfer arm 71, as shown in FIG.14A. Then, as shown in FIG. 14B, the transfer arm 71 is raised in thestate that the rear surface Wb of the processing target wafer W isattracted to and held by the attraction surface 71 a, so that theprocessing target wafer W is separated into the first separation waferW1 and the second separation wafer W2. In the process A5 as statedabove, the second separation wafer W2 is separated as one body with theperipheral portion We. That is, the removal of the peripheral portion Weand the separation (thinning) of the processing target wafer W areperformed at the same time.

The separated second separation wafer W2 is collected to, for example,the outside of the wafer processing system 1. By way of example, acollector (not shown) may be provided within a movable range of thetransfer arm 71, and the separated second separation wafer W2 may becollected by releasing the attraction of the second separation wafer W2in the collector.

In the present exemplary embodiment, the processing target wafer W isseparated by using the wafer transfer device 70 in the processingapparatus 80. However, a separation apparatus (not shown) for separatingthe processing target wafer W may be provided in the wafer processingsystem 1. This separation apparatus may be stacked on, for example, themodifying apparatus 60.

Next, the chuck 83 is moved to the processing position 80 b. Then, asshown in FIG. 7F, a rear surface W1 b as a separated surface of thefirst separation wafer W1 held by the chuck 83 is ground by the grindingunit 84, and the peripheral modification layer M1, the internalmodification layer M2, and the central modification layer M3 remainingon the rear surface W1 b are removed (process A6 of FIG. 6). In theprocess A6, by respectively rotating the first separation wafer W1 andthe grinding whetstone while keeping the grinding whetstone in contactwith the rear surface W1 b, the rear surface W1 b is ground. Further,the rear surface W1 b of the first separation wafer W1 may be thencleaned with a cleaning liquid by using a cleaning nozzle (not shown).

Subsequently, the combined wafer T is transferred to the cleaningapparatus 41 by the wafer transfer device 70. In the cleaning apparatus41, the rear surface W1 b of the first separation wafer W1 as theseparated surface is scrub-cleaned (process A7 of FIG. 6). Further, inthe cleaning apparatus 41, the rear surface Sb of the support wafer S aswell as the rear surface W1 b of the first separation wafer W1 may becleaned.

Afterwards, the combined wafer T is transferred to the etching apparatus40 by the wafer transfer device 50. In the etching apparatus 40, therear surface W1 b of the first separation wafer W1 as the separatedsurface is wet-etched by a chemical liquid (process A8 of FIG. 6). Agrinding mark may be formed on the rear surface W1 b ground by theaforementioned processing apparatus 80. In the process A8, the grindingmark can be removed by performing the wet-etching, so that the rearsurface W1 b can be flattened.

Then, the combined wafer T after being subjected to all the requiredprocessings is transferred to the transition device 30 by the wafertransfer device 50, and then transferred into the cassette Ct on thecassette placing table 10 by the wafer transfer device 20. Accordingly,a series of the processes of the wafer processing in the waferprocessing system 1 is ended.

In the above-described exemplary embodiment, the processing sequence ofthe processes A1 to A8 may be appropriately changed.

As a first modification example, the order of the formation of theperipheral modification layer M1 in the process A2 and the formation ofthe internal modification layer M2 in the process A3 may be reversed. Inthis case, the wafer processing is performed in the order of the processA1, the process A3, the process A2, and the processes A4 to A8.

As a second modification example, the formation of the centralmodification layer M3 in the process A4 may be performed before theformation of the peripheral modification layer M1 in the process A2. Inthis case, the wafer processing is performed in the order of the processA1, the process A4, the processes A2 and A3, and the processes A5 to A8.

As a third modification example, the formation of the centralmodification layer M3 in the process A4 may be performed before theformation of the internal modification layer M2 in the process A3. Inthis case, the wafer processing is performed in the order of theprocesses A1 and A2, the process A4, the process A3, and the processesA5 to A8.

As a fourth modification example, the formation of the non-bondingregion Ae in the process A1 may be performed after the formation of theperipheral modification layer M1 in the process A2. In this case, thewafer processing is performed in the order of the process A2, theprocess A1, and the processes A3 to A8.

As a fifth modification example, the formation of the non-bonding regionAe in the process A1 may be performed after the formation of theinternal modification layer M2 in the process A3. In this case, thewafer processing is performed in the order of the processes A2 and A3,the process A1, and the processes A4 to A8.

Further, in the above-described exemplary embodiment, the processings ofthe processes A1 to A8 may be appropriately omitted.

As a first example of the omission, the removal of the peripheralmodification layer M1, the internal modification layer M2 and thecentral modification layer M3 in the process A6 may be carried out bythe wet etching in the process A8. In this case, the grinding processingof the process A6 may be omitted.

As a second example of the omission, if the peripheral modificationlayer M1, the internal modification layer M2, and the centralmodification layer M3 are properly removed and no grinding mark isformed in the grinding processing of the process A6, the wet etching ofthe process A8 may be omitted.

As a third example of the omission, if the combined wafer T having thenon-bonding region Ae formed therein is carried into the waferprocessing system 1, the formation of the non-bonding region Ae in theprocess A1 may be omitted.

Further, if the non-bonding region Ae is performed after the alignmentof the processing target wafer W in the modifying apparatus 60 as in theabove-described modification examples 4 and 5, the above-describedmicro-alignment (calculation of the second eccentric amount between thecenter of the chuck 100 and the bonding region Ac by imaging theboundary of the non-bonding region Ae) may be omitted. In this case, theformation of the peripheral modification layer M1 in the process A2 maybe carried out based on the result of the macro-alignment.

Furthermore, in the process A5 of the above-described exemplaryembodiment, the second separation wafer W2 is separated as one body withthe peripheral portion We, that is, the removal of the peripheralportion We and the thinning of the processing target wafer W areperformed at the same time. However, the second separation wafer W2 andthe peripheral portion We do not have to be separated at the same time.For example, the second separation wafer W2 may be separated after theperipheral portion We is removed by the edge trimming. In this case, byallowing the crack C1 developing from the peripheral modification layerM1 formed in the process A2 to reach the front surface Wa and the rearsurface Wb as shown in FIG. 15A, the edge trimming processing and thethinning processing can be performed appropriately, as illustrated inFIG. 15B. There may be a case where the peripheral portion We need notbe removed. In this case, the alignment of the processing target wafer Wmay be performed by the outer end of the processing target wafer Winstead of the boundary between the bonding region Ac and thenon-bonding region Ae.

In addition, in the above-described exemplary embodiment, though boththe horizontal (Y-axis direction) movement in forming the internalmodification layer M2 and the horizontal (Y-axis direction) movement inperforming the eccentricity correction are performed by either the chuck100 or the laser head 110 on one axis, these horizontal movements may beperformed on two axes. By way of example, the laser head 110 may performthe horizontal movement for the formation of the internal modificationlayer M2, and the chuck 100 may perform the horizontal movement for theeccentricity follow-up. Alternatively, the chuck 100 may perform thehorizontal movement for the formation of the internal modification layerM2, and the laser head 110 may perform the horizontal movement for theeccentricity follow-up.

Now, the method of forming the internal modification layer M2 in theprocess A3 will be described. In the process A3, the internalmodification layer M2 is formed in the spiral shape, as stated above. Asshown in FIG. 16, an interval between the internal modification layersM2 adjacent in the circumferential direction will be referred to as acircumferential interval P (pulse pitch), and an interval between theinternal modification layers M2 adjacent in the diametrical directionwill be referred to as a diametrical interval Q (index pitch).

As described above, the internal modification layer M2 needs to beformed at the diametrically inner side than the peripheral modificationlayer M1 in order to suppress quality deterioration of the edge trim.However, when the centers of the chuck 100 and the processing targetwafer W are not coincident, that is, when the correction of the firstand second eccentric amounts by the control device 90 is not properlyperformed, the modification layers may be formed eccentrically withrespect to the processing target wafer W. When the modification layersis formed without taking such eccentricity into consideration, there isa likelihood that the internal modification layer M2 is formed at thediametrically outer side than the peripheral modification layer M1.

Thus, in the modifying apparatus 60, in order to suppress the internalmodification layers M2 from being formed at the diametrically outer sidethan the peripheral modification layer M1, eccentricity correction isperformed when forming the modification layers. Such eccentricitycorrection is carried out by moving the chuck 100 and the laser head 110in the horizontal directions (X-axis direction and Y-axis direction),for example.

FIG. 17 is an explanatory diagram showing a state of modification layersformed within the processing target wafer W by a first eccentricitycorrection method.

When the centers of the chuck 100 and the processing target wafer W donot coincide with each other, the non-bonding region Ae is formedeccentrically with respect to the processing target wafer W in theprocess A1. As stated above, the peripheral modification layer M1 isformed in a ring shape to be concentric with the bonding region Ac(non-bonding region Ae) in the process A2. Accordingly, in the processA3, the internal modification layers M2 are formed in the spiral shapealong the peripheral modification layer M1 to be concentric with thebonding region Ac and the peripheral modification layer M1. That is, inthe first eccentricity correction method, both the peripheralmodification layer M1 and the internal modification layers M2 are formedwhile the eccentricity correction thereof is performed.

As described above, according to the first eccentricity correctionmethod, by forming the internal modification layers M2 to be concentricwith the peripheral modification layer M1 which is formed to follow theeccentricity of the bonding region Ac, the formation of the internalmodification layers M2 at the diametrically inner side than theperipheral modification layer M1 can be suppressed.

As described in the first eccentricity correction method, it isdesirable that the internal modification layers M2 are formed to followthe eccentricity. If, however, the internal modification layers M2 areformed in the center portion of the processing target wafer W to followthis eccentricity, it is necessary to reciprocate the chuck 100 and thelaser head 110 in the horizontal directions at a high speed. As aresult, there are concerns that the eccentricity correcting operationmay not be able to keep up with the operation of forming the internalmodification layers M2, and resonance and guide lifetime may be reduced.Therefore, in a second eccentricity correction method to be describedbelow, the eccentricity correcting operation is not performed at leastin the center of the processing target wafer W.

FIG. 18 is an explanatory diagram showing a state of modification layersformed within the processing target wafer W by the second eccentricitycorrection method.

When the centers of the chuck 100 and the processing target wafer W arenot coincident, the non-bonding region Ae is formed eccentrically withrespect to the processing target wafer W in the process A1. As statedabove, the peripheral modification layer M1 is formed in the ring shapeto be concentric with the bonding region Ac (non-bonding region Ae) inthe process A2.

Subsequently, in the second eccentricity correction method, a bufferlayer B as a first internal modification layer for absorbing theeccentricity of the bonding region Ac is formed at a diametrically innerside of the processing target wafer W along the peripheral modificationlayer M1 while correcting the eccentricity of the chuck 100 (processingtarget wafer W). To elaborate, after the rotation speed of the chuck 100is rate-controlled (becomes constant) after its rotation is begun, thelaser light L is periodically radiated to the inside of the processingtarget wafer W from the laser head 110 while rotating the chuck 100(processing target wafer W) one round (360 degrees) at least, as shownin FIG. 19, so that the annular internal modification layer M2 isformed. Then, the laser head 110 is relatively moved inwards in thediametrical direction of the processing target wafer W (Y-axisdirection). By forming the internal modification layers M2 in the planedirection in a certain processing width while repeating the formation ofthe annular internal modification layer M2 and the inward movement ofthe laser head 110 in the diametrical direction, the internalmodification layers M2 as the buffer layer B are formed to be concentricwith the bonding region Ac and the peripheral modification layer M1, asillustrated in FIG. 18 and FIG. 19. Moreover, the buffer layer B isformed in the processing width (for example, 500 μm) equal to or largerthan the eccentric amount of the bonding region Ac, for example.

Further, the diametrical interval Q of the internal modification layersM2 in the buffer layer B may be set as required.

After the buffer layer B is formed, the internal modification layer M2as a second internal modification layer is formed in a spiral shape froma certain point within the processing width of the buffer layer B, forexample. In the formation of this spiral-shaped internal modificationlayer M2, the above-described eccentricity correction is not performed.That is, in the second eccentricity correction method, the internalmodification layers M2 of the concentric circle shapes forming thebuffer layer B and the peripheral modification layer M1 are formed whileperforming the eccentricity correction, whereas the spiral-shapedinternal modification layers M2 formed at the diametrically inner sidethan the buffer layer B are formed without performing the eccentricitycorrection.

As described above, according to the second eccentricity correctionmethod, by forming, at the diametrically inside of the peripheralmodification layer M1, the buffer layer B which is formed in theprocessing width equal to or larger than the eccentric amount of thebonding region Ac, it is not necessary to perform the eccentricitycorrection in the formation of the spiral-shaped internal modificationlayer M2. That is, even if the internal modification layer M2 is formedeccentrically, since the eccentric amount is absorbed in the processingwidth of the buffer layer B, the internal modification layer M2 does notextend to the diametrically outer side than the peripheral modificationlayer M1. Further, since the eccentricity correction need not beperformed in the formation of the internal modification layer M2, theinternal modification layer M2 can be formed more easily.

Further, by eliminating the need to perform the eccentricity correctionin the central portion of the processing target wafer W, theaforementioned failure in properly performing the eccentricitycorrection can be suppressed. Furthermore, the concerns for theoccurrence of resonance and the reduction of the guide lifetime can bereduced. Additionally, since the eccentricity correction is notperformed in the central portion as described above, the high rotationspeed of the chuck 100 can be maintained, and as a result, thecircumferential interval P of the internal modification layers M2 can beregulated constant.

FIG. 20 is an explanatory diagram illustrating a state of modificationlayers formed within the processing target wafer W by a thirdeccentricity correction method.

When the centers of the chuck 100 and the processing target wafer W arenot coincident, the non-bonding region Ae is formed eccentrically withrespect to the processing target wafer W in the process A1. Theperipheral modification layer M1 is annularly formed in the process A2to be concentric with the bonding region Ac (non-bonding region Ae) asstated above.

Subsequently, in the third eccentricity correction method, at thediametrically inner side than the peripheral modification layer M1 whichis annularly formed to be concentric with the bonding region Ac(non-bonding region Ae) in the process A2, eccentricity correction isperformed in a range where the laser head 110 is located at an outerperiphery of the processing target wafer W. That is, while moving thelaser head 110 from the diametrically outer side toward thediametrically inner side, the chuck 100 is rotated by the rotatingmechanism 103 so that the center of the chuck 100 and the center of thebonding region Ac coincide with each other, and, also, the chuck 100 ismoved in the Y-axis direction by the moving mechanism 104.

To elaborate, a formation range of the internal modification layer M2 inthe processing target wafer W is divided into a plurality of regionsalong the diametrical direction, and an eccentric stroke is reducedgradually along these regions. FIG. 20 illustrates an example where theformation range of the internal modification layers M2 is divided into acentral region R11 and four annular regions R12 to R15, and an eccentricamount of 100 μm is corrected by every 20 μm in each of the annularregions R12 to R15, that is, an example where the eccentric stroke isattenuated by 20 μm.

As described above, according to the third eccentricity correctionmethod, by performing the eccentricity correction in the range includedin the outer periphery of the processing target wafer W (the annularregions R12 to R15 in FIG. 20), it is not necessary to perform theeccentricity correction near the central portion of the processingtarget wafer W. That is, at the outer periphery of the processing targetwafer W, the above-described eccentricity correction (attenuation of theeccentric stroke) is completed, so the eccentric amount is 0 μm. In thecentral portion (central region R11 in FIG. 20), the centers of thechuck 100 and the bonding region Ac coincide with each other. Whenforming the internal modification layer M2 as described above, therotation speed of the chuck 100 is low when the laser head 110 islocated at the outer periphery of the processing target wafer W.Therefore, the eccentricity correction can be appropriately carried out.As a result, the eccentric amount can be absorbed, and the internalmodification layer M2 can be formed inside the peripheral modificationlayer M1. At this time, since the eccentricity correction is notperformed in the central portion, the high rotation speed of the chuck100 can be maintained, and, as a consequence, the circumferentialinterval P of the internal modification layer M2 can be controlledconstant.

Further, by removing the need to perform the eccentricity correction inthe central region R11 of the processing target wafer W, the failure inproperly performing the eccentricity correction as described above canbe suppressed. Furthermore, the concerns for the occurrence of theresonance and the reduction of the guide lifetime can be reduced.

Moreover, the number of the annular regions for performing theeccentricity correction is not limited to the example of the presentexemplary embodiment, and it can be selected as required. In addition,the eccentricity need not necessarily be corrected in a step manner forthe annular regions as in the present exemplary embodiment. Theeccentricity correction may be continuously performed from the outerperiphery of the processing target wafer W toward the center thereof. Asan example, the eccentricity correction may be performed for the timeduring which the laser head 110 radiates the laser light L severalrounds from the outer side of the processing target wafer W.

In addition, when correcting the eccentric amount at the outer peripheryof the processing target wafer W by the third eccentricity correctionmethod, it is desirable that the eccentricity correction is completed upto the half (r/2) of a radius of the processing target wafer W. That isto say, it is desirable that the radius of the central region R11 shownin FIG. 20 is equal to or larger than r/2.

The internal modification layer M2 in the process A3 is formed asdescribed above. In this way, by performing the eccentricity correctionin the formation of the internal modification layer M2, the edgetrimming processing and the thinning processing can be easily carriedout. Moreover, for this reason, it becomes easy to maintain the qualityof the edge trimming processing and the thinning processing, and controlin both processings can be simplified.

Now, the method of forming the central modification layer M3 in theprocess A4 will be elaborated.

As described above, in order to perform the separation of the processingtarget wafer W uniformly within the surface thereof, it is desirablethat a formation interval of the internal modification layers M2 isuniform. To control this formation interval to be constant, the rotationspeed of the chuck 100 and the frequency of the laser light L arecontrolled in the formation of the internal modification layers M2 inthe process A3.

However, when the rotation speed of the chuck 100 reaches an upper limitand the frequency of the laser light L reaches a lower limit, thecircumferential interval P of the internal modification layers M2reaches a threshold at which it can be no more enlarged. In this state,if the radiation position of the laser light L is moved inwards in thediametrical direction, the circumferential interval P decreases, so thatthe internal modification layers M2 may overlap on the same processingline in the central portion of the processing target wafer W. As aresult, the central portion of the processing target wafer W may not beproperly separated.

The reason why the central portion of the processing target wafer Wcannot be separated will be described in further detail. For example,when the internal modification layers M2 are formed to be overlapped,that is, when the radiation of the next (second) laser light L isoverlapped with the first formed internal modification layer M2, itbecomes difficult for the cracks C2 to develop in the diametricaldirection. For another example, even if the internal modification layersM2 are not overlapped, if the circumferential interval P is smaller thana certain threshold, the next (second) laser light L is radiated to thecracks C2 which is developing from the first formed internalmodification layer M2. In this case, since the laser light L is radiatedto the cracks C2 from which a stress is already released, it becomesdifficult again for the cracks C2 to develop in the diametricaldirection. For these reasons, since the cracks C2 may not be properlydeveloped in the central portion of the processing target wafer W, theremay arise a case when the central portion of the processing target waferW may not be separated.

Further, if the internal modification layers M2 are formed to beoverlapped as described above, transmitted light of the next (second)laser light L may be generated, and some of the laser light may betransmitted downwards, affecting the device layer D.

Thus, the present inventors have come up with a method of forming thecentral modification layer M3 as a way to separate the central portionof the processing target wafer W properly. That is, the formation of theinternal modification layer M2 is terminated near the central portion ofthe processing target wafer W where the circumferential interval Preaches the threshold, and the central modification layer M3 is formedat the diametrically inside of the internal modification layer M2, asillustrated in FIG. 21. A formation region R3 of the centralmodification layer M3 shown in FIG. 21 may be calculated from theminimum value of the frequency of the laser light L and the maximumvalue of the rotation speed of the chuck 100 (for example, a range ofabout 1 mm to 2 mm from the center of the processing target wafer W).

In this way, by terminating the formation of the internal modificationlayer M2 at the required position calculated from the rotation speed ofthe chuck 100 and the frequency of the laser light, the overlapping ofthe formed internal modification layers M2 can be suppressed so that theprocessing target wafer W can be separated properly, and generation ofthe transmitted light of the laser light L can be suppressed. Further,by forming the central modification layer M3 at the diametrically insideof the internal modification layers M2, the cracks C2 that develop fromthe internal modification layers M2 can be suppressed from beingconnected in the central portion of the processing target wafer W toform a protruding portion.

Furthermore, the central modification layer M3 may be formed to have anyof various shapes at the diametrically inside of the internalmodification layers M2. For example, although the central modificationlayer M3 is formed by a plurality of, for example, seven straight linesin the example shown in FIG. 21, the shape of the central modificationlayer M3 may not be limited thereto. By way of example, the centralmodification layer M3 may be formed by less than 7, for example, asshown in FIG. 22, only one straight line as long as the separation ofthe processing target wafer W in the central portion thereof can beperformed appropriately. As stated above, by reducing the number of thecentral modification layer M3 to be formed, tact for the formation ofthe central modification layer M3 can be reduced. Moreover, the shape ofthe central modification layer M3 is not limited to the straight lineshape, and it may be formed to have, for example, only a curved shape ora combination of the straight line shape and the curved shape.

Here, if processing lines of the central modification layers M3 areformed to cross each other, there is a likelihood that the multiplecentral modification layers M3 may be formed to overlap each other ortransmitted light of the laser light may be generated at thecorresponding intersection(s). In addition, if the central modificationlayers M3 are formed to be close to each other, the cracks C3 developingfrom these central modification layers M3 may be connected to eachother, resulting in formation of a protruding portion in the centralportion of the processing target wafer W, which in turn arises alikelihood that the flatness of the separated surface of the processingtarget wafer W may be deteriorated.

Thus, it is desirable that the processing lines of the centralmodification layers M3 are formed independently so as not to cross eachother or to be close to each other, as shown in FIG. 21, such that thecracks C3 developing from the adjacent central modification layers M3along the plane direction are not connected. Desirably, a formationinterval of the central modification layers M3 may be equal to or largerthan, e.g., 10 μm.

The central modification layers M3 in the process A4 are formed asdescribed above.

According to the second eccentricity correction method of the presentexemplary embodiment, by forming, at the diametrically inside of theperipheral modification layer M1, the buffer layer B to be concentricwith the peripheral modification layer M1 in the width larger than theeccentric amount between the chuck 100 and the processing target waferW, it is possible to appropriately form the spiral-shaped internalmodification layer M2. That is, even when the internal modificationlayer M2 is formed eccentrically with respect to the processing targetwafer W, the corresponding eccentric amount can be absorbed by thebuffer layer B, so that the formed internal modification layer M2 is notoverlapped with the peripheral modification layer M1. Accordingly, thequality of the edge trimming processing can be maintained.

Further, according to the present exemplary embodiment, it is notnecessary to perform the eccentricity correction in the central portionof the processing wafer W, that is, in the formation of thespiral-shaped internal modification layer M2. Thus, the control for theformation of the internal modification layer M2 can be simplified, andthe internal modification layer M2 can easily formed. In addition, sincethere is no need to perform the eccentricity correction in the centralportion of the processing target wafer W as described above, it ispossible to appropriately reduce the aforementioned concerns for theoccurrence of resonance and the reduction of the guide lifetime.

In addition, since the eccentricity correction need not be performed inthe central portion of the processing target wafer W as described above,it is easy to maintain the rotation speed of the chuck 100 in formingthe internal modification layer M2 in the central portion, and, as aresult, it is easy to regulate the circumferential interval P constant.That is, the separation of the processing target wafer W can beperformed uniformly within the surface thereof.

In addition, according to the above-described exemplary embodiment, theformation of the spiral-shaped internal modification layer M2 is startedfrom the certain point within the processing width of the buffer layerB. Although the starting position of the formation of the spiral-shapedinternal modification layer M2 can be selected as required, by formingit from the certain point within the processing width of the bufferlayer B in this way, it becomes possible to reduce the influence uponthe separation of the processing target wafer W while avoiding theinternal modification layer M2 from being formed at the diametricallyoutside of the peripheral modification layer M1. To be specific, since aregion where the internal modification layer M2 is not formed can bereduced, the processing target wafer W can be separated appropriately.

Further, in the present exemplary embodiment, since the internalmodification layer M2 is formed in the spiral shape without being cut inthe middle within the surface of the processing target wafer W, the tactfor the formation of the internal modification layer M2 can be improved.

Further, according to the above-described exemplary embodiment, theinternal modification layers M2 are formed such that the circumferentialinterval P and the diametrical interval Q are uniform within the surfaceof the processing target wafer W. However, the formation interval of theinternal modification layers M2 may not be limited thereto.

FIG. 23A and FIG. 23B are explanatory diagrams illustrating a method offorming the internal modification layer M2 according to a secondexemplary embodiment. As shown in FIG. 23A and FIG. 23B, in the surfaceof the processing target wafer Win which the internal modification layerM2 according to the second exemplary embodiment is formed, there areformed areas where the diametrical intervals Q between the internalmodification layers M2 are different. Specifically, a wide-intervalregion R1 in which the diametrical interval Q between the neighboringinternal modification layers M2 is set to be wide is formed at adiametrically outer side of the processing target wafer W, and anarrow-interval region R2 in which the diametrical interval Q betweenthe neighboring internal modification layers M2 is set to be narrow isformed at a diametrically inner side than the wide-interval region R1.Further, the circumferential interval P of the internal modificationlayer M2 is constant over the entire circumference both in thewide-interval region R1 and the narrow-interval region R2.

In addition, in the following description, the internal modificationlayer M2 formed in the wide-interval region R1 may sometimes be referredto as an outer modification layer M2 e, and the internal modificationlayer M2 formed in the narrow-interval region R2 may sometimes bereferred to as an inner modification layer M2 c.

Here, in the wide-interval region R1, a formation interval Q1 of theneighboring outer modification layers M2 e is set such that the cracksC2 which develop in the plane direction during the formation of theseneighboring outer modification layers M2 e are not connected to eachother, as shown in FIG. 23B. The outer modification layers M2 e arestarted to be formed from a certain point within the processing width ofthe buffer layer B and are formed at the diametrically inside of thebuffer layer B. Further, in the narrow-interval region R2, a formationinterval Q2 of the neighboring inner modification layers M2 c is set sothat the cracks C2 which develop in the plane direction during theformation of these neighboring inner modification layers M2 c areconnected to each other, as shown in FIG. 23B. As an example, theformation interval Q1 of the outer modification layers M2 e may be 60μm, and the formation interval Q2 of the inner modification layers M2 cmay be 10 μm.

Further, the internal modification layer M2 is formed by radiating thelaser light to the inside of the processing target wafer W to amorphize(polycrystallize) the portion to which the laser light is radiated. Atthis time, in the internal modification layer M2, a compressive stressis generated, as shown in FIG. 24A. Here, in the wide-interval regionR1, since the cracks C1 of the adjacent outer modification layers M2 eare not connected, the generated compressive stress is accumulated inthe outer modification layers M2 e. Accordingly, a tensile stressresulting from the compressive stress are accumulated between the outermodification layers M2 e adjacent in the diametrical direction, as shownin FIG. 24A. Regions in which the tensile stress acts (hereinafterreferred to as the “tensile regions U”) are annularly formed over theentire circumference of the processing target wafer W, as shown in FIG.24B.

Now, a method of forming the wide-interval region R1 and thenarrow-interval region R2 as described above, and a method of separatingthe processing target wafer W will be described. FIG. 25 is a flowchartshowing main processes of the method of forming the internalmodification layers M2 in the process A3 and the method of separatingthe processing target wafer W. FIG. 26A to FIG. 26E are explanatorydiagrams schematically showing the main processes of the method offorming the internal modification layers M2 in the process A3 and themethod of separating the processing target wafer W. Each of FIG. 26A toFIG. 26E illustrates a cross section of the half of the processingtarget wafer W in the diametrical direction, seen from a thicknessdirection thereof. In addition, in FIG. 26A to FIG. 26E, illustration ofthe support wafer S is omitted for the simplicity of illustration.

In addition, the peripheral modification layer M1 and the cracks C1 areformed in the processing target wafer W prior to the formation of theinternal modification layer M2 (process A2 in FIG. 6 and FIG. 25).Further, the internal modification layer M2 as the buffer layer B isformed. A method of forming the buffer layer B is the same as theabove-described exemplary embodiment.

As depicted in FIG. 26A, in the formation of the internal modificationlayer M2, the wide-interval region R1 is first formed (process A3-1 ofFIG. 25). By rotating the chuck 100 (processing target wafer W) andmoving the laser head 110 in the Y-axis direction from the diametricallyouter side of the processing target wafer W toward the diametricallyinner side thereof, the wide-interval region R1 is formed sequentiallyfrom the diametrically outer side of the processing target wafer Wtoward the diametrically inner side thereof. The formation interval Q1of the outer modification layers M2 e is, for example, 60 μm. Here, thecracks C2 that develop from the adjacent outer modification layers M2 ein the wide-interval region R1 are not connected. Further, the formationof the outer modification layers M2 e is begun from, for example, thecertain point within the processing width of the buffer layer B.

Here, since the cracks C2 are not connected to each other, thecompressive stresses are accumulated in the internal modification layersM2, and the tensile regions U are formed between the adjacent internalmodification layers M2, as stated above.

After the wide-interval region R1 is formed, the narrow-interval regionR2 is formed, as illustrated in FIG. 26B (process A3-2 of FIG. 25). Thenarrow-interval region R2 is formed sequentially from the center of theprocessing target wafer W toward the diametrically outer side thereof byrotating the chuck 100 (processing target wafer W) and moving the laserhead 110 in the Y-axis direction from the diametrically inner side ofthe processing target wafer W toward the diametrically outer sidethereof. The formation interval Q2 of the inner modification layers M2 cis, for example, 10 μm. Here, the cracks C2 that develop from theadjacent inner modification layers M2 c in the narrow-interval region R2are connected to each other sequentially.

Further, as illustrated in FIG. 26B, in the formation of thenarrow-interval region R2 in the process A3-2, the crack C2 of the innermodification layer M2 c located on the outermost side of thenarrow-interval region R2 and the crack C2 of the outer modificationlayer M2 e located on the innermost side of the wide-interval region R1are not connected.

Further, the inner modification layer M2 c is not formed in the centralportion of the processing target wafer W where the circumferentialinternal P cannot be maintained.

After the narrow-interval region R2 is formed, a starting pointmodification layer M2 s serving as a starting point for the start of theseparation of the processing target wafer W is formed, as depicted inFIG. 26C. Specifically, the internal modification layer M2 as thestarting point modification layer M2 s is formed between thewide-interval region R1 and the narrow-interval region R2. Accordingly,the crack C2 of the inner modification layer M2 c located on theoutermost side of the narrow-interval region R2 and the crack C2 of theone outer modification layer M2 e positioned on the innermost side ofthe wide-interval region R1 are connected.

If the starting point modification layer M2 s is formed, the cracks C2of the wide-interval region R1 and the narrow-interval region R2 areconnected, so that the compressive stress accumulated in the one outermodification layer M2 e of the wide-interval region R1 is released.Then, by this release of the stress, the one outer modification layer M2e swells in a direction in which the first separation wafer W1 and thesecond separation wafer W2 are detached, as shown in FIG. 26D. That is,at the position where the corresponding one outer modification layer M2e is formed, the first separation wafer W1 and the second separationwafer W2 are detached with the crack C2 as the boundary (process A3-4 ofFIG. 25).

In this way, if the first separation wafer W1 and the second separationwafer W2 are detached at the position where the corresponding one outermodification layer M2 e is formed, the crack C2 develops outwards in thediametrical direction, as shown in FIG. 26D, while being affected by theforce acting in the thickness direction (detachment direction) of theprocessing target wafer W due to the detachment. As a result, this crackC2 is connected to the crack C2 which is developing from another outermodification layer M2 e adjacent thereto (process A3-5 of FIG. 25).

If the cracks C2 of the one outer modification layer M2 e and theanother outer modification layer M2 e are connected, the compressivestress accumulated in the another outer modification layer M2 e isreleased. Then, by this release of the stress, the first separationwafer W1 and the second separation wafer W2 are detached with the crackC2 as the boundary at the position where the another outer modificationlayer M2 e is formed (process A3-5 of FIG. 25).

Then, if the first separation wafer W1 and the second separation waferW2 are detached in this way at the position where the another outermodification layer M2 e is formed, the crack C2 is made to furtherdevelop outwards in the diametrical direction while being affected bythe force acting in the thickness direction (detachment direction) ofthe processing target wafer W due to the detachment.

As the development of the crack C2, the release of the compressivestress, and the detachment of the second separation wafer W2 arerepeated in a chain reaction in this way, the crack C2 reaches theperipheral modification layer M1, as illustrated in FIG. 26E (processA3-6 of FIG. 25).

If the internal modification layers M2 are formed in the entire surfaceof the processing target wafer W while the cracks C2 develop as statedabove, the formation of the internal modification layers M2 in theprocess A3 is completed. Then, the central modification layer M3 isformed at the diametrically inside of the inner modification layers M2 c(process A4 in FIG. 6 and FIG. 25), and the peripheral portion We andthe second separation wafer W2 are removed thereafter (process A5 inFIG. 6 and FIG. 25).

According to the above-described second exemplary embodiment, theinternal modification layers M2 are formed in the processing targetwafer W, and these internal modification layer M2 are divided into thewide-interval region R1 and the narrow-interval region R2. In thewide-interval region R1, the detachment of the first separation wafer W1and the second separation wafer W2 takes place in the chain reaction asstated above.

As stated above, according to the above-described exemplary embodiment,a gap is formed in the thickness direction within the processing targetwafer W due to the detachment of the first separation wafer W1 and thesecond separation wafer W2. That is, since a region in which the firstseparation wafer W1 and the second separation wafer W2 are not connectedis formed within the surface of the processing target wafer Was shown inFIG. 26E, the force required for the subsequent detachment of the secondseparation wafer W2 is reduced.

In addition, according to the above-described exemplary embodiment, byenlarging the diametrical interval Q of the internal modification layersM2 in the wide-interval region R1, the number of the internalmodification layers M2 to be formed can be reduced. Thus, the timerequired for the formation of the internal modification layers M2 can bereduced, so that the throughput can be further improved.

Further, according to the above-described exemplary embodiment, thefirst separation wafer W1 and the second separation wafer W2 in thewide-interval region R1 are separated along the crack C2 that naturallydevelops by the release of the accumulated stress to be used as thestarting point of the separation. For this reason, especially in thewide-interval region R1, a smooth separated surface having a periodicstructure can be obtained.

FIG. 27A provides a captured image of a separated surface of theprocessing target wafer W when the diametrical interval Q of theinternal modification layers M2 is set to be uniform within the surfaceof the processing target wafer W, and FIG. 27B shows a captured image ofa separated surface of the processing target wafer W when the internalmodification layers M2 are formed to have the wide-interval region R1and the narrow-interval region R2. As can be seen from FIG. 27A and FIG.27B, by forming the wide-interval region R1 and the narrow-intervalregion R2 while allowing the cracks C2 to naturally develop by therelease of the accumulated stress, the surface roughness after theseparation is ameliorated, and the smooth separated surface can beobtained.

In addition, in the above-described second exemplary embodiment as well,the buffer layer B is formed, and the spiral-shaped internalmodification layers M2 (the outer modification layers M2 e and the innermodification layers M2 c) are formed from the certain point within theprocessing width of the buffer layer B. Accordingly, even when the outermodification layers M2 e are formed eccentrically with respect to theprocessing target wafer W, these outer modification layers M2 e do notoverlap the peripheral modification layer M1. Therefore, the quality ofthe edge trimming processing can be maintained.

Moreover, according to the above-described second exemplary embodiment,the wide-interval region R1 is formed at the diametrically outer side,and the narrow-interval region R2 is formed at the diametrically innerside. As shown in FIG. 28A, however, the narrow-interval region R2 maybe formed at the diametrically outer side of the processing target waferW, and the wide-interval region R1 may be formed inside thisnarrow-interval region R2, when viewed from the top. As another example,as shown in FIG. 28B, the wide-interval region R1 and thenarrow-interval region R2 may be alternately formed at the diametricallyouter side of the processing target wafer W.

Further, in the above-described second exemplary embodiment, thewide-interval region R1 and the narrow-interval region R2 are formedwith respect to the diametrical direction of the processing target waferW, that is, the diametrical interval Q of the internal modificationlayers M2 is changed. Instead, however, the circumferential interval P(pulse pitch) may be changed. Moreover, both the diametrical interval Qand the circumferential interval P may be changed. In such a case, sincethe number of the internal modification layers M2 to be formed withinthe surface of the processing target wafer W is further reduced, thethroughput can be further improved.

Further, in the above-described second exemplary embodiment, theseparation of the processing target wafer W is started by forming thestarting point modification layer M2 s between the wide-interval regionR1 and the narrow-interval region R2. However, the way how to start theseparation of the processing target wafer W is not limited thereto. Byway of example, after forming the wide-interval region R1 up to apredetermined position from the diametrically outer side of theprocessing target wafer W toward the diametrically inner side thereof asshown in FIG. 29A, the separation may be begun by forming thenarrow-interval region R2 from the center of the processing target waferW toward the diametrically outer side thereof to be joined with theinternal modification layer M2 of the wide-interval region R1, asillustrated in FIG. 29B.

It should be noted that the above-described exemplary embodiment isillustrative in all aspects and is not anyway limiting. Theabove-described exemplary embodiment may be omitted, replaced andmodified in various ways without departing from the scope and the spiritof claims.

EXPLANATION OF CODES

60: Modifying apparatus

90: Control device

110: Laser head

L: Laser light

B: Buffer layer

M1: Peripheral modification layer

M2: Internal modification layer

W: Processing target wafer

1. A processing apparatus configured to process a processing targetobject, comprising: a modifying device configured to radiate laser lightto an inside of the processing target object to form multiplemodification layers along a plane direction of the processing targetobject; and a controller configured to control an operation of themodifying device at least, wherein the controller controls the modifyingdevice to form: a peripheral modification layer which serves as astarting point where a peripheral portion of the processing targetobject as a removing target is detached; a first internal modificationlayer in a ring shape to be concentric with the peripheral modificationlayer at a diametrically inner side than the peripheral modificationlayer; and a second internal modification layer in a spiral shape at adiametrically inner side than the first internal modification layer. 2.The processing apparatus of claim 1, wherein the controller controls themodifying device such that a processing width of the first internalmodification layer in a diametrical direction is larger than aneccentric amount between a center of the processing target object and acenter of a holder configured to hold the processing target object. 3.The processing apparatus of claim 1, wherein the controller controls themodifying device such that a formation of the second internalmodification layer is begun from a point within a processing width ofthe first internal modification layer in a diametrical direction.
 4. Aprocessing method of processing a processing target object, comprising:forming, by a modifying device, multiple modification layers along aplane direction of the processing target object by radiating laser lightto an inside of the processing target object held by a holder, whereinthe forming of the multiple modification layers comprises: forming aperipheral modification layer which serves as a starting point where aperipheral portion of the processing target object as a removing targetis detached; forming a first internal modification layer in a ring shapeto be concentric with the peripheral modification layer at adiametrically inner side than the peripheral modification layer; andforming a second internal modification layer in a spiral shape at adiametrically inner side than the first internal modification layer. 5.The processing method of claim 4, wherein the forming of the firstinternal modification layer comprises: forming the first internalmodification layer to be concentric with the peripheral modificationlayer by radiating the laser light to the inside of the processingtarget object from the modifying device periodically while rotating theprocessing target object held by the holder relative to the modifyingdevice; moving the modifying device relative to the holder in adiametrical direction; and forming the first internal modification layerin the ring shape along the plane direction by repeating the forming ofthe first modification layer which is concentric with the peripheralmodification layer and the moving of the modifying device in thediametrical direction.
 6. The processing method of claim 4, wherein thefirst internal modification layer is formed in a processing width largerthan an eccentric amount between a center of the holder and a center ofthe processing target object in a diametrical direction.
 7. Theprocessing method of claim 6, wherein the forming of the second internalmodification layer is begun from a point within the processing width ofthe first internal modification layer in the diametrical direction. 8.The processing method of claim 4, wherein the forming of the secondinternal modification layer comprises: forming the second internalmodification layer in the spiral shape along the plane direction byradiating the laser light to the inside of the processing target objectfrom the modifying device periodically while rotating the processingtarget object held by the holder relative to the modifying device and,also, by moving the modifying device relative to the holder in adiametrical direction.